Modem analytical instruments are particularly susceptible to performance variations due to the thermal sensitivity of certain components that operate within the analytical instrument. The temperature of one or more components of an analytical instrument is typically controlled by locating the component in a temperature controlled environment, or thermal zone. The temperature of the thermal zone is typically effected by an electrically-powered heating and/or cooling device.
One particular type of analytical instrument is a chromatograph. The basic components of a chromatograph include an injection port for introducing a sample of matter to be examined into a stream of carrier medium, a separation column attached to the injection port that causes some of the constituents of the sample to elute at different times, and a detector for producing a signal indicative of the presence of the constituents being eluted. An integrator may be employed for integrating the signal so as to provide information as to the quantity of each constituent.
In the typical chromatograph, the temperature controlled zone is constructed as an oven. The injection port and detector are attached to respective pneumatic fittings on the oven, and the separation column is attached between the pneumatic fittings and located within the oven. The oven typically comprises an insulated oven housing, a controlled heating element, and a stirring fan. The stirring fan continuously mixes the air contained within the oven housing so as to minimize temperature gradients therein that could adversely affect the performance of the chemical process occurring within the column. During a typical sample analysis, the heating element is operated so as to increase the temperature of the oven from a minimum initial value to a maximum final value. Before introduction of the next sample into the column, the temperature of the oven is usually returned to its initial value. With repeated use of the heating unit, fan, and other such devices, the chromatograph requires a considerable amount of power to operate.
Accordingly, a conventional chromatograph is best suited for use in the laboratory and similar settings where adequate electrical power is available. There have been attempts to reduce the size and complexity of a chromatograph so as to be practical outside of the laboratory. See, for example, Terry et al., "A Gas Chromatographic Air Analyzer Fabricated on a Silicon Wafer", IEEE Trans. Electron Devices, Dec. 1979.) Such miniaturization has not been fully realized, due in part to an unresolved need for a compact, reliable, and efficient system for providing one or more of the requisite thermal zones in the instrument.